Examples of cleaning and degreasing methods that have been applied to metals, ceramics, plastics, and other materials in the past can include alkali cleaning, cleaning with a surface active agent, cleaning with chloro-solvent, and/or cleaning with a fluoro-solvent. Alkali cleaning is cleaning achieved by dipping the material into a warm aqueous solution or alcohol solution of sodium hydroxide or other alkali agent, or by spraying such a solution. Cleaning with a surface active agent is achieved by dipping the material into a warm aqueous solution of a surface active agent, or by spraying such a solution. Cleaning with chloro-solvent involves dipping or vapor cleaning by using a chloro-solvent, such as, for example, 1,1,1-trichloroethane, trichloroethylene, and perchloroethylene. Finally, cleaning with a fluoro-solvent involves dipping or vapor cleaning, such as, for example, by using Freon 113.
Currently, organic solvents used in cleaning processes for various materials include hydrocarbons, halogenated hydrocarbons, propylene and ethylene glycol ethers, esters, or mixtures thereof. These solvents are useful since they can be recycled within the process by distillation. However, during the cleaning process, since closed-loop cleaning machines internally recycle the organic solvents by distillation, volatile acids which are brought in and/or generated in the cleaning process are often not removed from the cleaning fluid and therefore can enrich over time. These acids can be harmful to the machine and/or the cleaned parts.